Degree days are units used to predict the development or life cycle stage of organisms based on what?

• A. All of the above
• B. Plants
• C. Insects
• D. Disease-causing organisms

Answer: (D)

Degree days measure heat accumulation over time, using temperatures above a threshold to estimate when an organism reaches a specific developmental stage. For disease-causing organisms, this is especially useful because their growth, infection capacity, and reproduction depend on temperature. By summing daily temperatures that exceed the threshold, you can forecast when pathogens are likely to become active or reach stages that threaten turf health, allowing you to time preventive actions (like fungicide applications or sanitation) before disease develops. While plants and insects also respond to degree days, this concept is particularly valuable for predicting disease activity and managing outbreaks.